J. B. S. Haldane once famously quipped that "God is inordinately fond of beetles." Results of a study suggest that this fondness was expressed not by making so many, but rather by allowing them to persist for so long.
In a study appearing in the American Naturalist, scientists show that many insect groups like beetles and butterflies have fantastic numbers of species because these groups are so old. In contrast, less diverse groups, like mammals and birds, are evolutionarily younger.
This is a surprisingly simple answer to a fundamental biological puzzle. They accumulated data from molecular phylogenies (which date the evolutionary relationships among species using genetic information) and from the fossil record to ask whether groups with more species today had accumulated species at faster rates.
Animals as diverse as mollusks, insects, spiders, fish, amphibians, reptiles, birds, and mammals appear to have accumulated new species at surprisingly similar rates over evolutionary time. Groups with more species were simply those that had survived longer. Their analyses thus identify time as a primary determinant of species diversity patterns across animals.
Given the unprecedented extinction rates that the Earth's biota are currently experiencing, these findings are also quite sobering. We are rapidly losing what it has taken nature hundreds of millions of years to construct, and only time can repair it.
Wednesday, August 15, 2007
Tuesday, August 14, 2007
Stopping Cancer Cells From Reading Their Own DNA
There are three primary ways of treating cancer at present, and these have fundamentally changed little in 30 years. If there are tumours, surgery can be used to cut out the cancerous tissue, It the cells are malignang, then radiation therapy is the method. Chemotherapy is used to keep the cancerous cells from dividing. But a new approach using a molecular technique to prevent interference in the DNA copy metric.
The approach uses the information from tumor cells and block them from copying DNA sequences. This will cut off the genetic information flow that tumours need to grow.
The enzyme called Topoisomerase IB plays a key role in some of the molecular metric involved in the processes of DNA and RNA copying during cell division. These are responsible for reading the genetic code and making sure it is encoded correctly in the daughter cell. In healthy cells this process works normally, but in cancer cells it does not work well at all. If one can specifically target these molecular metrics in cancer cells one can prevent the cancer cells from growing into a larger tumor.
This molecular copying metric is constructed largely out of proteins. It works by effectly walking along the DNA double helix reading the genetic code so that it can be copied accurately into new DNA during division. Other components is responsible for slicing and assembling the DNA itself.
The approach uses the information from tumor cells and block them from copying DNA sequences. This will cut off the genetic information flow that tumours need to grow.
The enzyme called Topoisomerase IB plays a key role in some of the molecular metric involved in the processes of DNA and RNA copying during cell division. These are responsible for reading the genetic code and making sure it is encoded correctly in the daughter cell. In healthy cells this process works normally, but in cancer cells it does not work well at all. If one can specifically target these molecular metrics in cancer cells one can prevent the cancer cells from growing into a larger tumor.
This molecular copying metric is constructed largely out of proteins. It works by effectly walking along the DNA double helix reading the genetic code so that it can be copied accurately into new DNA during division. Other components is responsible for slicing and assembling the DNA itself.
Monday, August 13, 2007
Genetic evidence for evolution
If there is evolution, is there any evidence for it at the genetic level?
The answer is yes. Scientists who have been studying genetic changes occurring in the human genome over the last 15,000 to 100,000 years, have found that over this relatively short period of time the human genome has changed by as much as 10 percent.
Evidence withing the Human Genome
A scientific study identifies small, gradual changes (microevolution) that demonstrate species divergence from a common ancestor millions of years ago (macroevolution). The study makes human-to-human comparisons throughout the complete human genome instead of comparing a human to mice or chimpanzees. By this procedure humans can be seen changing over time, due to our ancestors being exposed to – among other selective pressures – different climates as they spread across the globe.
Evidence for Change
Early humans had problems digesting lactose after the age of one. Lactose is an enzyme found in milk. Befor the domestication of animals (about 20,000 years ago) humans could not digest milk after infancy. But some time after humans began migrating and domesticating animals, humans began to develop a gene that allowed us to tolerate consuming milk into adulthood. In other words as humans have populated the world, there has been strong selective pressure at the genetic level for mutations that allow digestion of a new food source or tolerate infection by a pathogen that the population may not have faced in a previous environment.
The answer is yes. Scientists who have been studying genetic changes occurring in the human genome over the last 15,000 to 100,000 years, have found that over this relatively short period of time the human genome has changed by as much as 10 percent.
Evidence withing the Human Genome
A scientific study identifies small, gradual changes (microevolution) that demonstrate species divergence from a common ancestor millions of years ago (macroevolution). The study makes human-to-human comparisons throughout the complete human genome instead of comparing a human to mice or chimpanzees. By this procedure humans can be seen changing over time, due to our ancestors being exposed to – among other selective pressures – different climates as they spread across the globe.
Evidence for Change
Early humans had problems digesting lactose after the age of one. Lactose is an enzyme found in milk. Befor the domestication of animals (about 20,000 years ago) humans could not digest milk after infancy. But some time after humans began migrating and domesticating animals, humans began to develop a gene that allowed us to tolerate consuming milk into adulthood. In other words as humans have populated the world, there has been strong selective pressure at the genetic level for mutations that allow digestion of a new food source or tolerate infection by a pathogen that the population may not have faced in a previous environment.
Sunday, August 12, 2007
Trilobite variation declined after the Cambrian Explosion
From an evolutionary perspective, the more variable a species is, the more raw material natural selection has to operate on. So a highly variable species will evolve more rapidly than others.
Is that statement true?
Paleontologists for decades have suspected that highly variable species evolved more rapidly than others, and several studies have approached questions pertaining to it--but this is the first to convincingly document it in any group.
Most studies have focused on the variability that occurs between species rather than within them, but one recent study analyzed 982 species of trilobites, ancient relatives of spiders and horseshoe crabs.
When did Trilobites live?
Trilobites have been extinct for over 250 million years. They were once the most common creatures in the world's oceans. They ranged in size from nearly microscopic to more than a foot long, though most of the 17,000 known species measured from one to four inches. They were very diverse.
Trilobites were among the creatures that emerged 500 million years ago, during what paleontologists call "the Cambrian explosion," or "the Cambrian radiation." Before this time, life on Earth was limited mostly to bacteria, algae, single-celled organisms and only the simplest animal groups. But during the Cambrian Period, more complex creatures with skeletons, eyes and limbs emerged with amazing suddenness.
What does the research show?
So the question is what fueled the Cambrian radiation, and why was that event so singular? The answer: It appears that organisms displayed "rampant" within-species variation in the 'warm afterglow' of the Cambrian explosion, but not later.
A study focused on actively evolving characteristics during the Cambrian time. The trilobite head alone displayed many different characteristics. There were differences in ornamentation, number and placement of spines, and the shape of head segments. Overall, approximately 35 percent of the 982 trilobite species exhibited some variation in some aspect of their appearance that was evolving. But more than 70 percent of early and middle Cambrian species exhibited variation, while only 13 percent of later trilobite species did so.
Conclusion: There's hardly any variation in the post-Cambrian. Even the presence or absence or the kind of ornamentation on the head shield varies within these Cambrian trilobites and doesn't vary in the post-Cambrian trilobites.
Why does variation withing a species decline through time?
Paleontologists have proposed two ideas to account for why variation within species declined through time.
1)Ecological. In the very early Cambrian seas, fewer organisms existed than today, which meant that they faced less competition for food. You didn't really have to be tightly specialized to make a living in the Cambrian. But as evolution gave rise to more varieties of organisms, ecological communities became more diverse. You had to be very fine-tuned to your particular niche to make a living and to beat out competitors for a limited resource. More organizms in the ocean meant that there must be more genetic variation in order to survive.
2) The genomic hypothesis offers a second explanation for the decline of within-species variation over time. According to this idea, internal processes in the organism were the key factors. Various developmental processes interact with one another to control the growth and formation of body parts as any organism progresses from egg to adult.
It's been suggested that early on in evolutionary history, in the Cambrian Period, the degree to which these different developmental processes interacted with each other within the organism was a lot less. As a result, the constraints on what the final organism looked like were relatively low.
Is that statement true?
Paleontologists for decades have suspected that highly variable species evolved more rapidly than others, and several studies have approached questions pertaining to it--but this is the first to convincingly document it in any group.
Most studies have focused on the variability that occurs between species rather than within them, but one recent study analyzed 982 species of trilobites, ancient relatives of spiders and horseshoe crabs.
When did Trilobites live?
Trilobites have been extinct for over 250 million years. They were once the most common creatures in the world's oceans. They ranged in size from nearly microscopic to more than a foot long, though most of the 17,000 known species measured from one to four inches. They were very diverse.
Trilobites were among the creatures that emerged 500 million years ago, during what paleontologists call "the Cambrian explosion," or "the Cambrian radiation." Before this time, life on Earth was limited mostly to bacteria, algae, single-celled organisms and only the simplest animal groups. But during the Cambrian Period, more complex creatures with skeletons, eyes and limbs emerged with amazing suddenness.
What does the research show?
So the question is what fueled the Cambrian radiation, and why was that event so singular? The answer: It appears that organisms displayed "rampant" within-species variation in the 'warm afterglow' of the Cambrian explosion, but not later.
A study focused on actively evolving characteristics during the Cambrian time. The trilobite head alone displayed many different characteristics. There were differences in ornamentation, number and placement of spines, and the shape of head segments. Overall, approximately 35 percent of the 982 trilobite species exhibited some variation in some aspect of their appearance that was evolving. But more than 70 percent of early and middle Cambrian species exhibited variation, while only 13 percent of later trilobite species did so.
Conclusion: There's hardly any variation in the post-Cambrian. Even the presence or absence or the kind of ornamentation on the head shield varies within these Cambrian trilobites and doesn't vary in the post-Cambrian trilobites.
Why does variation withing a species decline through time?
Paleontologists have proposed two ideas to account for why variation within species declined through time.
1)Ecological. In the very early Cambrian seas, fewer organisms existed than today, which meant that they faced less competition for food. You didn't really have to be tightly specialized to make a living in the Cambrian. But as evolution gave rise to more varieties of organisms, ecological communities became more diverse. You had to be very fine-tuned to your particular niche to make a living and to beat out competitors for a limited resource. More organizms in the ocean meant that there must be more genetic variation in order to survive.
2) The genomic hypothesis offers a second explanation for the decline of within-species variation over time. According to this idea, internal processes in the organism were the key factors. Various developmental processes interact with one another to control the growth and formation of body parts as any organism progresses from egg to adult.
It's been suggested that early on in evolutionary history, in the Cambrian Period, the degree to which these different developmental processes interacted with each other within the organism was a lot less. As a result, the constraints on what the final organism looked like were relatively low.
Saturday, August 11, 2007
A Complete primate gene study
U.S. scientists have completed what's believed the most comprehensive assessment of gene copy number variations across human and non-human primate species.
A study provides an overview of genes and gene families that have undergone major copy number expansions and contractions during approximately 60 million years of evolutionary time.
Primates first appeared on Earth about 90 million years ago, and today roughly 300 primate species exist. To survey the differences in gene copy number among those species, researchers used DNA microarrays containing more than 24,000 human genes to perform comparative genomic hybridization experiments. DNA comparisons were made using samples from humans with those of nine other primate species: chimpanzee, gorilla, bonobo, orangutan, gibbon, macaque, baboon, marmoset, and lemur. This allowed them to identify specific genes and gene families that, through evolutionary time, have undergone lineage-specific copy number gains and losses.
The scientists said they discovered differences potentially associated with cognition, reproduction, immune function, and susceptibility to genetic disease.
A study provides an overview of genes and gene families that have undergone major copy number expansions and contractions during approximately 60 million years of evolutionary time.
Primates first appeared on Earth about 90 million years ago, and today roughly 300 primate species exist. To survey the differences in gene copy number among those species, researchers used DNA microarrays containing more than 24,000 human genes to perform comparative genomic hybridization experiments. DNA comparisons were made using samples from humans with those of nine other primate species: chimpanzee, gorilla, bonobo, orangutan, gibbon, macaque, baboon, marmoset, and lemur. This allowed them to identify specific genes and gene families that, through evolutionary time, have undergone lineage-specific copy number gains and losses.
The scientists said they discovered differences potentially associated with cognition, reproduction, immune function, and susceptibility to genetic disease.
Friday, August 10, 2007
Shrinking Genomes
Scientists generally believe that insertions of retroelements, or"jumping genes," once established in a population, are irreversible and are maintained throughout evolution. This unidirectional theory of retroelement evolution, which calls for ever-expanding genome size, is challenged by work that appears in the September issue of Genome Research.
Deletion of Genome elements from Rhesus to Humans
Researchers performed a whole-genome comparison of the human, chimpanzee, and Rhesus monkey sequences, and they identified 37 instances where a retroelement was present in Rhesus (a more primitive primate species) but absent in either humans or chimpanzees. This indicated that these retroelements had been deleted during the evolution of the more recent primate species.
Mediation by short identical sequences
Intriguingly, the scientists further demonstrated that these deletions were mediated by short identical sequences that flank the retroelements. They extended the study to random, non-retroelement sequences and showed that deletions caused by short identical DNAsequences were a widespread genomic phenomenon. In fact, thousands of insertion-deletion sequence differences between the human and chimpanzee genomes were likely mediated by short identical sequences.
The work strongly suggests an important role for short, non-adjacent, identical segments of DNA in genomic deletions and it lends insight into deletion mechanisms that help to counterbalance genome expansion in primates.
Conclusion: Genes don't get bigger with more complex species, they get smaller.
Deletion of Genome elements from Rhesus to Humans
Researchers performed a whole-genome comparison of the human, chimpanzee, and Rhesus monkey sequences, and they identified 37 instances where a retroelement was present in Rhesus (a more primitive primate species) but absent in either humans or chimpanzees. This indicated that these retroelements had been deleted during the evolution of the more recent primate species.
Mediation by short identical sequences
Intriguingly, the scientists further demonstrated that these deletions were mediated by short identical sequences that flank the retroelements. They extended the study to random, non-retroelement sequences and showed that deletions caused by short identical DNAsequences were a widespread genomic phenomenon. In fact, thousands of insertion-deletion sequence differences between the human and chimpanzee genomes were likely mediated by short identical sequences.
The work strongly suggests an important role for short, non-adjacent, identical segments of DNA in genomic deletions and it lends insight into deletion mechanisms that help to counterbalance genome expansion in primates.
Conclusion: Genes don't get bigger with more complex species, they get smaller.
Thursday, August 9, 2007
Ecological Biogeography
Unlike historical biogeographers, ecological biogeographers make extensive use of current population information. They study the ways in which species develop and interact in the presence of other species and different environments. Many ecological biogeographers mimic Darwin: they study island communities as a type of experimental system to test hypotheses about species development.
Much of ecological biogeography is concerned with species richness, the number of different species an area supports. In specific, ecological biographers have developed the species richness equilibrium model.
The model begins with an uninhabited "island" that can be either a literal island or an area of like habitats completely surrounded by unlike habitats. All species available to colonize the new area are called the "species pool." As more and more new species enter the new area, the species pool becomes smaller and smaller, and the immigration rate (the probability that any given species moving into the area will be a new species) decreases.
At the same time, the island becomes more and more crowded and supplies become scarce, causing the extinction rate to increase. The point at which the extinction rate and the immigration rate balance is called the equilibrium point. The model predicts that changes in extinction and immigration rates will tend toward the equilibrium point, which is different for every island, depending on resources and degree of separation from other areas. This is shown graphically in the figure below.
Much of ecological biogeography is concerned with species richness, the number of different species an area supports. In specific, ecological biographers have developed the species richness equilibrium model.
The model begins with an uninhabited "island" that can be either a literal island or an area of like habitats completely surrounded by unlike habitats. All species available to colonize the new area are called the "species pool." As more and more new species enter the new area, the species pool becomes smaller and smaller, and the immigration rate (the probability that any given species moving into the area will be a new species) decreases.
At the same time, the island becomes more and more crowded and supplies become scarce, causing the extinction rate to increase. The point at which the extinction rate and the immigration rate balance is called the equilibrium point. The model predicts that changes in extinction and immigration rates will tend toward the equilibrium point, which is different for every island, depending on resources and degree of separation from other areas. This is shown graphically in the figure below.
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